The best known unsaturated diacids or diesters are those comprising chains comprising from 4 to 6 carbon atoms, such as the C4 acids maleic acid and fumaric acid, the C5 acids citraconic acid, mesaconic acid and itaconic acid and the C6 acids 2-methyleneglutaric acid and muconic acid. On the other hand, as regards long-chain diacids, the only ones having a degree of importance are dimers, generally obtained by condensation of unsaturated carboxylic acids. The properties, syntheses and uses of these diacids are described in Ullmann's Encylopedia, Vol. A8, pages 533-536.
Saturated diacids are obtained industrially by various methods, all of which, however, exhibit some disadvantages. A great variety of these methods is enlarged upon in the above reference on pages 523-536.
It is possible to distinguish therein methods by degradation, such as ozonolysis or oxidation, of vegetable fatty acids.

The ozonolysis of oleic acid, of petroselinic acid and of erucic acid makes it possible to respectively produce the diacids comprising 9, 6 and 13 carbon atoms according to the above reaction process for petroselinic acid.
Another example is the cleavage of ricinoleic acid by the action of sodium hydroxide at a temperature of greater than 180° C. This method, used industrially, makes it possible to obtain the diacid comprising 10 carbon atoms. The same method, as illustrated in the scheme below, can be applied to lesquerolic acid and results in the formation of a diacid comprising 12 carbon atoms. This method exhibits the advantage of using renewable starting materials but is restricted essentially to the C10 diacid, lesquerolic acid being still not very widespread, and thus this method is relatively little used.

Mention may also be made of the oxidative degradation of monocarboxylic acids by the action of N2O4. The oxidation of stearic acid makes it possible to obtain a mixture of sebacic acid and of caprylic acid; suberic acid can be obtained from palmitic acid.
It is also possible to obtain diacids from smaller molecules by using variant techniques of carbonylation.
Finally, mention may be made of the fermentation, by a yeast, a fungus or a bacterium, of paraffin hydrocarbon or saturated or unsaturated fatty acid or ester substrates, which makes it possible to oxidize the compounds of the substrate. This method is well known. It is illustrated in particular in the paper by W. H. Eschenfeldt et al., “Transformation of Fatty Acids Catalyzed by Cytochrome P450 Monooxygenase Enzymes of Candida tropicalis”, and patents FR 2 445 374, U.S. Pat. No. 4,474,882, U.S. Pat. No. 3,823,070, U.S. Pat. No. 3,912,586, U.S. Pat. No. 6,660,505, U.S. Pat. Nos. 6,569,670 and 5,254,466. It makes it possible to obtain numerous diacids of variable chain length.
In the chemical industry and in particular the polymer industry, such as the production of polyamides of diacids/diamines type or of industrial polymers, it is necessary to have available a whole range of saturated or unsaturated diacids. These diacids will constitute starting materials which can in addition be converted to diamines of the same chain length by a simple chemical reaction. The unsaturated diacids will be used as monomers for specialty polymers.
It is therefore necessary to find a type of process which makes it possible to obtain a virtually complete range of saturated or unsaturated diacids and which, in addition, uses renewable materials of natural origin.